Bimetallic thermometer > General

The bimetallic thermometer is based on the phenomenon of linear expansion of metals with temperature. Based on the fact that two different metals change their dimensions unequally when the temperature varies, the bimetallic thermometer consists of two juxtaposed metal sheets, forming a single piece and generally in a helical shape. One end of the helix is ​​fixed and the other is connected to a pointer that can rotate freely on a graduated circular scale. To build a bimetallic thermometer, Invar (64% Fe-36% Ni) is normally used as a metal with a low coefficient of expansion and brass as a metal with a high coefficient of expansion. However, for higher temperatures, nickel is also used as a metal with a high coefficient of thermal expansion.

These thermometers have similar applications to glass thermometers, however, because they are resistant, they can be used in more demanding working conditions. They are used to measure temperatures in the range of -50 to + 500 ºC with an accuracy of ± 1%, where fast responses are not required.

Installation recommendations

– Always use a metal protective well to prevent corrosion, provide mechanical protection and allow maintenance while the process is in operation.
– At low temperatures, the bimetallic thermometer housing must be hermetically sealed to prevent moisture penetration and the formation of ice, damaging the instrument’s internal components.
– To avoid errors due to ambient temperature, the bimetallic must be completely immersed in the fluid.
– The fluid velocity must be high enough to ensure rapid heat transfer.